1. Field of the Invention
The present invention relates to the separation of gas and liquid from gas-liquid mixtures on a continuous basis, and relates more specifically to downhole gas anchors employed in oil and gas wells.
2. Description of the Related Art
In oil and gas reservoirs, petroleum oil is frequently found in intimate association with natural gas, both in the form of free gas bubble entrained in the oil and in the form of dissolved gas in the oil. Water is also commonly present in the reservoir fluids. Thus, well fluids commonly comprise both liquids and gas. In wells where pumping is necessary, the presence of this gas-liquid mixture materially affects the efficiency of pumping operations. In addition to the free gas in the mixture, the pressure decrease inherent at the suction of the pump inlet causes some of the dissolved gas to form more bubbles of free gas. The bubbles of free gas occupy part of the displacement of the pump, which results in reduced pumping efficiency. If the quantity of gas accumulates to a sufficient proportion, it will expand and contract to such a degree that the pump becomes gas locked, unable to cycle it's its flow control valves, and unable to pump any liquids at all.
A downhole reciprocating rod pump is the most common type of well pump being used today. Typically, the downhole rod pump is suspended by the tubing string and driven by a reciprocating surface unit through a string of sucker rods. The downhole pump is mounted at the bottom of the tubing string and pumps well liquids to the surface through the tubing string, while gas occupies an annulus between the tubing string and the well casing. The suction inlet of the pump is positioned below the liquid level in the well. In wells where bubbles of gas are present, it is known in the art to use a “gas anchor” to continuously separate the gas from the liquids before the liquid enters the inlet of the pump, the liquids being directed to the suction inlet of the pump and the gas being directed to the annulus. Thus, the gas anchor is typically connected to the suction inlet of the downhole pump, and is therefore located just below the pump itself. The efficiency of the separation of liquid and gas by the gas anchor is a critical aspect of the gas anchor design, and it should be noted that no gas anchor is totally effective in this separation process.
In addition to the gas-liquid separation efficiency of the gas anchor, it should be appreciated that the gas anchor is typically located thousands of feet below the surface, so reliability is also critically important. It is further important for a gas anchor design to facilitate its insertion and removal from the well bore casing using convention oil field service systems and techniques. It is further important to address the practicalities of well field operations, including abusive handling practices, oil fluid impurities, solids, abrasion, and unexpected failure of other well components. Given the high value of efficient oil well production, the expense of operating and maintaining wells, and the cost of servicing well, it can readily be appreciated that there is a need in the art for cost effective, reliable, and efficient gas-liquid separators.